From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A4CC4C76195 for ; Fri, 24 Mar 2023 09:31:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230196AbjCXJbZ (ORCPT ); Fri, 24 Mar 2023 05:31:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37402 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230023AbjCXJbY (ORCPT ); Fri, 24 Mar 2023 05:31:24 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 279691ACF4 for ; Fri, 24 Mar 2023 02:30:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1679650243; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=21j5HZHNaqnqYk/qMb/3bvONholuvmzFTx+bQH+Yn+o=; b=h4LU+l3zYuS6MYCtSl+weDUAmxL4XBHHhstguV+0y0Oo0IhQ5W19UkS+ERe196dqWbAKAx 7iL7k/UEoVaLEg8AqeLLKamISxpSrLENaCFGzPJpXpJBEaJ8IG0wwtd27/SUQ1LimaPn/k 5+JkJqik2sFOrhdl29O30BjWjS7YGzI= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-596-cWdaXyzfMFalnbgLRIuhDA-1; Fri, 24 Mar 2023 05:30:42 -0400 X-MC-Unique: cWdaXyzfMFalnbgLRIuhDA-1 Received: by mail-wm1-f70.google.com with SMTP id m7-20020a05600c4f4700b003ee7e120bdfso755644wmq.6 for ; Fri, 24 Mar 2023 02:30:41 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679650241; h=content-transfer-encoding:in-reply-to:organization:from:references :cc:to:content-language:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=21j5HZHNaqnqYk/qMb/3bvONholuvmzFTx+bQH+Yn+o=; b=LoayCPNB4F3QA5jCKrky8c2kpoFgKqQkkF1GicrCgYxROxdPh8v7JOWZJH4N59zpyr 7MM8kkkpCJq5L5rKDGN5cXwKEE/t+g1VoClGir0ZapzFyhR12fLxdR5oNLNQUNwhHgTj eYJMqjWVw5vOf788O5iCb2Y10F0oV4H4GkU52Wq9MczLr4nwmeAjg6e7RS3wbXKwKROH BR4Q4B2WlYbE9txAXF5RMhKt0+R/pXS8ljxB7Pc8EdDTwJvD+bf3OfT0HnUdF3peXBAG wfheKG64PTSAUOZrbAHszVqExSu5UhLaTzv2AnNuercDGO2ePi49dCbgYT+KgeLmluwe R+Ew== X-Gm-Message-State: AO0yUKX4mNM7j4SvOOHuPjFVOoJQyt13ka6VvAmAtIJBc2jYqtK+Qg+2 BZ9sBC3VQm0zl3N7jQP2JkW1kBtTqoIgPgdwSOnDfuI8iezaykEIzArXhgNPwFhhV1Xn09J/OJA ywEAA9lggHXF3Tf2M9BM2 X-Received: by 2002:a05:600c:2289:b0:3df:e468:17dc with SMTP id 9-20020a05600c228900b003dfe46817dcmr1727269wmf.40.1679650240909; Fri, 24 Mar 2023 02:30:40 -0700 (PDT) X-Google-Smtp-Source: AK7set/IiMAnVG44QY0lj4W/8T78wkjWb5uNZDBeaBMhsRJC8+SM5VO0asITh0DvQ+GzWK5qGo9Tvg== X-Received: by 2002:a05:600c:2289:b0:3df:e468:17dc with SMTP id 9-20020a05600c228900b003dfe46817dcmr1727251wmf.40.1679650240530; Fri, 24 Mar 2023 02:30:40 -0700 (PDT) Received: from [10.105.158.254] ([88.128.92.189]) by smtp.gmail.com with ESMTPSA id ay6-20020a05600c1e0600b003ee443bf0c7sm1318153wmb.16.2023.03.24.02.30.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Mar 2023 02:30:39 -0700 (PDT) Message-ID: <91d02705-1c3f-5f55-158a-1a68120df2f4@redhat.com> Date: Fri, 24 Mar 2023 10:30:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: FW: [LSF/MM/BPF TOPIC] SMDK inspired MM changes for CXL To: Kyungsan Kim Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-cxl@vger.kernel.org, a.manzanares@samsung.com, viacheslav.dubeyko@bytedance.com, dan.j.williams@intel.com References: <5536d792-867d-6390-81e2-b1ef135d347d@redhat.com> <20230324092731.148023-1-ks0204.kim@samsung.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230324092731.148023-1-ks0204.kim@samsung.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org On 24.03.23 10:27, Kyungsan Kim wrote: >> On 24.03.23 10:09, Kyungsan Kim wrote: >>> Thank you David Hinderbrand for your interest on this topic. >>> >>>>> >>>>>> Kyungsan Kim wrote: >>>>>> [..] >>>>>>>> In addition to CXL memory, we may have other kind of memory in the >>>>>>>> system, for example, HBM (High Bandwidth Memory), memory in FPGA card, >>>>>>>> memory in GPU card, etc. I guess that we need to consider them >>>>>>>> together. Do we need to add one zone type for each kind of memory? >>>>>>> >>>>>>> We also don't think a new zone is needed for every single memory >>>>>>> device. Our viewpoint is the sole ZONE_NORMAL becomes not enough to >>>>>>> manage multiple volatile memory devices due to the increased device >>>>>>> types. Including CXL DRAM, we think the ZONE_EXMEM can be used to >>>>>>> represent extended volatile memories that have different HW >>>>>>> characteristics. >>>>>> >>>>>> Some advice for the LSF/MM discussion, the rationale will need to be >>>>>> more than "we think the ZONE_EXMEM can be used to represent extended >>>>>> volatile memories that have different HW characteristics". It needs to >>>>>> be along the lines of "yes, to date Linux has been able to describe DDR >>>>>> with NUMA effects, PMEM with high write overhead, and HBM with improved >>>>>> bandwidth not necessarily latency, all without adding a new ZONE, but a >>>>>> new ZONE is absolutely required now to enable use case FOO, or address >>>>>> unfixable NUMA problem BAR." Without FOO and BAR to discuss the code >>>>>> maintainability concern of "fewer degress of freedom in the ZONE >>>>>> dimension" starts to dominate. >>>>> >>>>> One problem we experienced was occured in the combination of hot-remove and kerelspace allocation usecases. >>>>> ZONE_NORMAL allows kernel context allocation, but it does not allow hot-remove because kernel resides all the time. >>>>> ZONE_MOVABLE allows hot-remove due to the page migration, but it only allows userspace allocation. >>>>> Alternatively, we allocated a kernel context out of ZONE_MOVABLE by adding GFP_MOVABLE flag. >>> >>>> That sounds like a bad hack :) . >>> I consent you. >>> >>>>> In case, oops and system hang has occasionally occured because ZONE_MOVABLE can be swapped. >>>>> We resolved the issue using ZONE_EXMEM by allowing seletively choice of the two usecases. >>> >>>> I once raised the idea of a ZONE_PREFER_MOVABLE [1], maybe that's >>>> similar to what you have in mind here. In general, adding new zones is >>>> frowned upon. >>> >>> Actually, we have already studied your idea and thought it is similar with us in 2 aspects. >>> 1. ZONE_PREFER_MOVABLE allows a kernelspace allocation using a new zone >>> 2. ZONE_PREFER_MOVABLE helps less fragmentation by splitting zones, and ordering allocation requests from the zones. >>> >>> We think ZONE_EXMEM also helps less fragmentation. >>> Because it is a separated zone and handles a page allocation as movable by default. >> >> So how is it different that it would justify a different (more confusing >> IMHO) name? :) Of course, names don't matter that much, but I'd be >> interested in which other aspect that zone would be "special". > > FYI for the first time I named it as ZONE_CXLMEM, but we thought it would be needed to cover other extended memory types as well. > So I changed it as ZONE_EXMEM. > We also would like to point out a "special" zone aspeact, which is different from ZONE_NORMAL for tranditional DDR DRAM. > Of course, a symbol naming is important more or less to represent it very nicely, though. > Do you prefer ZONE_SPECIAL? :) I called it ZONE_PREFER_MOVABLE. If you studied that approach there must be a good reason to name it differently? -- Thanks, David / dhildenb